The present invention relates to a torque control apparatus for a permanent magnet motor, and in particular relates to the control apparatus for a permanent magnet motor capable of suppressing a torque ripple when there is a reluctance torque and there is an induced voltage distortion in an induced voltage waveform and thereby realizing an accurate torque control.
As the method of suppressing a torque ripple when the induced voltage of a magnet motor has a square waveform (the induced voltage distortion), there is known a method comprising the steps of converting a three-phase induced voltage waveform into a voltage ed of a d-axis and a voltage eq of a q-axis and calculating a current command value Iqref of the q-axis (canceling the torque ripple) according to Formula (1), as in the description of JPA-2004-201487.
                              I          qref                =                              2            3                    ⁢                      (                                          T                ref                            ×                                                ω                  m                                                  e                  q                                                      )                                              (        1        )            Where    Tref: a torque command value, and    ωm: the mechanical angle velocity of a motor.
That is, even if the induced voltage waveform of a magnet motor is a square waveform, the current command value Iqref of the q-axis containing a ripple waveform is calculated so as to set the output torque to be constant.
If vector control is performed according to this current command value, the torque ripple can be suppressed.
Formula (2) is the output torque formula of a magnet motor.
                              τ          m                =                              3            2                    ·                      P            m                    ·                      [                                                            K                  ed                                ·                                  I                  q                                            -                                                K                  eq                                ·                                  I                  d                                            +                                                (                                                            L                      d                                        -                                          L                      q                                                        )                                ⁢                                                      I                    d                                    ·                                      I                    q                                                                        ]                                              (        2        )            Where    Pm: the number of pole pairs of a motor,    Ked: the induced voltage coefficient of the d-axis,    Keq: the induced voltage coefficient of the q-axis,    Id: the current of the d-axis,    Iq: the current of the q-axis,    Ld: the inductance value of the d-axis, and    Lq: the inductance value of the q-axis.
The method described in JP-A-2004-201487 is a technique corresponding to a non-salient pole type (Ld=Lq) magnet motor with no reluctance torque, wherein the “induced voltage coefficients Ked, Keq” are distorted. Therefore, this method cannot be directly applied to the salient pole type (Ld<Lq) magnet motor.